Endothelium-derived relaxing factors are known to play a key role in vasorelaxation. At least two different factors have been identified: endothelium-derived relaxing factor (EDRF, thought to be nitric oxide or a closely related compound) and endothelium-derived hyperpolarizing factor (EDHF). The mechanisms by which these substances produce relaxation remains incompletely understood. The goal of this research is to understand the effects of endothelium-derived factors on ion channels in arterial smooth muscle. Recent studies have suggested that EDHF, acting via arterial smooth muscle potassium channels, may be responsible for as much as 50% of endothelium-derived vasorelaxation. Furthermore, there are reports that EDRF may also affect ion channels in arterial smooth muscle, but the species of channels affected remains poorly defined. Previous studies on endothelium-dependent relaxation have provided an incomplete picture of the ionic mechanisms involved for two reasons: Intact segments of artery are very difficult to voltage clamp; and, only pharmacological vasodilators rather than endothelium-derived substances have been studied in isolated patch clamped cells. We propose to patch clamp cells isolated from rabbit cerebral and systemic arteries and to test the effects of endothelial effluent from a column of cultured bovine aortic endothelial cells on ion channels. The properties and pharmacology of the channel(s) affected by endothelial-derived factors will be identified. There are four specific aims: 1) What are the effects of endothelial factors on ion channels in arterial smooth muscle? 2) What are the effects of vasoconstrictors on these ion currents? 3) What is the nature of the endothelial factors that produce these effects? 4) What are the signal transduction pathways involved? By investigating the effects of endothelial-derived factors on isolated vascular smooth muscle ion channels with patch clamp techniques, we will determine new aspects of this important facet of endothelial control of vascular tone. These studies will lead to better understanding of vascular control in health and in disease states.